Exact observer-based structures for arbitrary compensators

In this paper, some new techniques for determining the observer-based or LQ G form of any compensator with arbitrary order are discussed. The practical appeal of such techniques is that they allow for a simplified implementati on and reduced memory storage of general controllers and offer additional f lexibility for handling gain-scheduling and input saturation constraints as compensator states become meaningful variables. The derived observed-based controllers are input-output equivalent to the original controller but wit h an explicit separated estimation/control structure. Such structures invol ve both static control and estimation gains with an extra Youla parameter t hat can be either static or dynamic. The proposed techniques are applicable both in continuous and discrete time, to full-order controllers, that is, controllers whose order is the same as the plant's order but also to augmen ted- and reduced-order controllers whose orders are greater or smaller, res pectively. Necessary conditions to apply this general controller equivalenc e principle are derived. The interest and practicality of such techniques are then investigated with regards to the LQG implementation of H-infinity and mu controllers, classe s or controllers that do not generally enjoy ease of implementations. (C) 1 999 John Wiley & Sons, Ltd.